Circuit interruptions with non-linear resistance



Nov. 19, 1957 T. o. EATON 2,813,953

CIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Filed Aug. 16, 1954 5Sheets-Sheet l INVENTOR. EE- 1 7mm Mm mv wb Nov. 19, 1957 T. o. EATON2,813,953

CIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Filed Aug. 16, 1954 3Sheets-Sheet 2 E5. 5. E. 5a-

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CIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Filed Aug. 16, 1954 3Sheets-Sheet 3 IN V EN TOR. E. 5- 7211; 0- 'flranl ited States PatentCIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Temple 0. Eaton,Narberth, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia,Pa., a company of Pennsylvania Application August 16, 1954, Serial No.449,989 1 Claim. (Cl. 200-147) My invention relates to circuitinterrupters and is more particularly directed to a novel arrangementwherein a non-linear resistance is used to decrease the rate of increaseand decrease of the fault current as it passes through zero in order tofacilitate the extinguishing of the arc. The magnitude of the resistanceis such at low voltage that the current and voltage will be in phasemaking the best conditions for are interruptions.

Circuit breakers of the prior art have been provided with linearresistance which is inserted in the circuit after an arc is drawn. Thatis, when rated current is flowing through the cooperating contacts ofthe circuit interrupter, the auxiliary resistor is not in the circuit.However, on the occurrence of a fault current, when the cooperatingcontacts separate and an arc is drawn between, the auxiliary resistanceis automatically inserted in the circuit. This resistance serves tolimit the maximum value which will be reached by the fault current. Thatis, the magnitude of the let through current does not reach theavailable short circuit current value due to the large magnitude ofresistance which is inserted at the instant of circuit interruption.

Although this prior art arrangement serves to limit the maximummagnitude which the fault current will reach, it does not substantiallyalter the rate of increase or decrease of the current as it passesthrough zero and hence, does not substantially aid in interrupting thearc. That is, it merely limits the maximum magnitude of current so asnot to subject the network being protected by the circuit interrupterfrom the extreme magnitude of the available short circuit current butdoes not substantially aid in the interruption of the arc.

In my novel arrangement I have provided a non-linear resistance which isinserted in the circuit when an arc is drawn. The non-linear resistancehas the characteristics of a maximum magnitude of resistance when thevoltage is zero or minimum and has a minimum magnitude of resistancewhen the voltage is large.

Thus, assuming that the voltage and current are in phase (i. e. 100%power factor), the magnitude of resistance will be at its minimum valuewhen the voltage is at its maximum value. Hence, the fault current mayreach the available short circuit current value since the magnitude ofresistance is relatively small at that instant.

However, when the voltage is passing through zero, due to the non-linearcharacteristics of the resistor, the magnitude of the resistance will bemaximum and hence will cause the current to hesitate or step as it goesthrough zero. That is, it will be substantially decreased in the rate ofincrease or decrease of the current as it passes through zero. Hence,the current will remain about the zero value for a longer period oftime. Also there is a substantial reduction in the ionization of thegases so that the arc chute will have a longer period of time and betterconditions to extinguish the are when it is at its minimum magnitude.

In the event that the current and voltage are not in 'ice phase, i. e.either an inductive or capacitive network, then the insertion of a largemagnitude of resistance as the voltage passes through zero will tend toimprove the power factor that is decrease the degree of current lead orlag and thus facilitate the extinguishing of the arc as above noted.

Accordingly a primary object of my invention is to provide a novelarrangement wherein a non-linear resistance is inserted in the networkimmediately following the initial contact separation.

Another object of my invention is the provision of a resistance,inserted in the circuit when an arc is drawn, which will have a maximummagnitude of resistivity when the voltage is at a minimum value tothereby decrease the rate of current increase or decrease as it passesthrough zero and thereby provide a longer period of time for the arc tobe extinguished by the arc chute when the current is at its minimumvalue.

These and other objects of my invention will be apparent when taken inconnection with the drawings in which:

Figure 1 is a side view of a circuit interrupter and illustrates themanner in which a non-linear resistor is inserted in series with theblow-out coil. In the first embodiment of Figure l the non-linearresistor is connected between the stud of the stationary contacts andthe blowout coil.

Figure 2 is a plot of voltage vs. current and illustrates the non-linearcharacteristics of the resistor used in my novel system.

Figure 2A is a characteristic curve of the non-linear resistor used inmy invention and is a plot of resistance vs. voltage.

Figure 3 is a schematic circuit diagram of a resistive network.

Figure 3A is an oscillogram of voltage and current vs. time and thecircuitry of Figure 3 and illustrates the hesitation or step of thefault current as it passes through zero.

Figure 4 is a schematic circuit diagram of an inductive network.

Figure 4A is an oscillogram of voltage and current vs. time and thecircuitry of Figure 4 and illustrates the hesitation or step of thefault current as it passes through zero.

Figure 5 is a side view of the circuit interrupter similar to that ofFigure 1 and illustrates a modification of the embodiment thereinwherein the non-linear resistor is connected in series between the studof the movable contact and the arc runner and the front are horn of thearc chute.

Referring now to the figures in Figure l I have shown a side view of atypical circuit breaker to which my invention may be applied. Thecircuit breaker shown in Figure 1 may be of the type shown in co-pendingapplication Serial No. 307,843 filed September 4, 1952, now Patent No.2,761,934, issued Sept. 4, 1956, and has the following components: astud 10 to which the stationary main contact 11 is connected and a lowerstud 12 on which the movable contact arm 13 is pivoted at 17. Themovable contact arm 13 is biased to an open position (not shown) and ismoved to the closed position by means of linkage l4 and 15. The links 14and 15 are pivotally secured to each other at 16 and the link 14 ispivotally connected to the movable contact arm 13. The movable contactarm contains the main movable contact 18, first moving arcing contact 19and the second moving arcing contact 20. These contacts makerespectively with the main stationary contact 11, the first stationaryarcing contact 21 and the second stationary arcing contact 22 when acircuit breaker is moved to the closing position by means of the linkage1415.

An arc chute 23 is mounted above the cooperating contacts and isprovided with a back arcing horn 26 and a front arcing horn 24. The backarcing horn 26 is received by the disconnect contacts when the arc chute23 is pushed in place. The disconnect contacts 25 are connected by meansof a lead 27 to the blow-out coil 28 and is mounted on the magnetic core29 which has a U-shaped configuration and slits the arc chute 23.

The opposite end of the blow-out coil 28 is connected by means ofconductor 31 to the non-linear resistor 33 which in turn is connected bymeans of the conductor 32 to the upper stud 10. When the main contacts1118 of the circuit breaker are in engagement, the current will flowfrom the upper stud 10 through the main stationary contact 11 to themain movable contact arm 13 to the lower stud 12. Hence, when normalcurrent is flowing through the line with the circuit breaker contacts inengagement, the non-linear resistor is out of the circuit.

The non-linear resistor 30 has the characteristics illustrated inFigures 2 and 2A wherein the magnitude of resistance is at a maximumvalue when the voltage is at a minimum value and the magnitude ofresistance is at a minimum value when the voltage is at a maximum value,as clearly seen in Figure 2A. Thus, as seen in Figure 2, in the plot ofcurrent versus voltage, the non-linear characteristics of the resistor30 will cause the current to hesitate or step as it passes through zeroalthough there is no time lag between applied voltage and resultingcurrent.

That is, since the magnitude of the non-linear resistor 30 is extremelyhigh at the time that the voltage is at a zero or minimum value, it willinfluence the magnitude and rate of current at that time. The non-linearresistor 30 may be made of a material known in the trade as Thyrite,which is described in Calculation of Circuits Containing Thyrite, byTheodore Brownlee, G. E. Review, volume 37, No. 4, pages 175-179 andpages 218 223 of volume 37, No. 5; Thyrite: A New Material for LightningArrestors, by K. B. McEachron, General Electric Review, vol. 33, No. 2,pages 9299, and Performance of Thyrite Arrester for Any Assumed Form ofTraveling Wave and Circuit Arrangement, by K. B. McEachron and H. G.Brinton, General Electric Review, June 1930, page 350.

On the occurence of a fault current a trip coil will be sufiicientlyenergized to initiate the separation of the cooperating contacts as iswell known in the circuit interrupter art. At the first instant when themain cooperating contacts 11-18 separate the current will be divertedthrough the first set of arcing contacts 2119. That is, since the member33 which carries the movable arcing contact 19 is pivotally mounted at34 on the movable contact arm 13 the initial separation will drive thefirst movable arcing contact 19 into engagement with the firststationary arcing contact 21.

Hence, the circuit will be energized through upper stud 10, through thefirst set of arcing contacts 21-19, through the member 33, throughmovable contact arm 13 and to the lower stud 12. As the contact arm 13continues to rotate in a clockwise direction about its pivot 17 the arcwill be transferred from the first set of arcing contacts 2119 to thesecond set of arcing contacts 222). The insulator 35 is positionedbetween the first arcing contact 21 and the second arcing contact 22introduces an air gap between these two members so that the arc will notexist between the arcing contact 21 and the arcing contact 22 untilthere is a sufficient air gap between the arcing con tacts 21-19.

Thus, in this position the current will flow from the upper stud 10 tothe first arcing contact 21. An arc will exist from the first arcingcontact 21 to the second stationary arcing contact 22 and from thiscontact to the second movable arcing contact 20 through the conductingmember 33 to the movable contact arm 13 and then to the lower stud 12.

Upon continued movement of the movable contact arm 13 toward the openposition the arcing horn 33 of the movable member will engage the frontarcing horn 24. At this time the current will be diverted through analternate path which consists of the conductor 32, the non-linearresistor 30, through the conductor 31, the blow-cut coil 28 through theconductor 27 through the disconnect contacts 25, the back arcing horn 26through the arc chute 23 to the front arcing horn 24 to the movablearcing horn 33 and then through the movable contact arm 13 to the lowerstud 12.

Hence, it is only after an arc is drawn and the current diverted throughthe blow-out coil 28 that the non-linear resistor 39 is introduced intothe circuit.

if the circuit being protected by the circuit breaker of Figure l isresistive, then Figure 3 represents a schematic diagram of same whereinthe source 36 having a voltage 2 supplies the short circuit line throughthe non-linear resistor 30.

In Figure 3A I have illustrated the oscillograrn of the voltage andcurrent vs. time when the non-linear resistor 30 is inserted in thecircuit.

As heretofore noted when the voltage is at a minimum or zero value theresistance of the non-linear resistor 39 will be at a maximum value asillustrated in Figure 2A. As seen in Figure 2 the current will be causedto step or hesitate at the time that the voltage is at its zero orminimum value. Thus, the oscillogram of Figure 3A clearly illustratesthis condition existing in the circuitry of Figure 3.

Since the rate of current increase and decrease is decreased as itpasses through zero magnitude there will be a longer period of time thatthe current is at its minimum value and also a substantial reduction inthe ionization of the gases within the arc chute 23. Hence, the arcinterrupting device 23 will have both a longer period of time and moredesirable conditions over which to extinguish the arc which has beenmoved therein by means of the blow-out coil 28.

In Figure 4 I have illustrated the schematic network diagram for aninductive circuit which may be protected by the circuit breaker such asin Figure 1. The circuit diagram of Figure 4 is that which exists afterthe nonlinear resistor 30 has been inserted in the circuit. Theinductance of the line is represented by the lumped inductor 37.

In Figure 4A I have illustrated the voltage and current conditions whichwould exist in a network such as illustrated in Figure 4. Since a veryhigh magnitude of resistance is inserted in the circuit at the time anarc is drawn and the current is flowing through the blow-out coil theresistance will have the efiect of bringing the current in closer phaserelationship with the voltage. That is, there will be a substantialincrease in the power factor.

Hence, as clearly seen in Figure 4A there will be a substantialhesitation or step of the current as it passes through zero even thoughthere is not a power factor.

It will be noted that the above desirable conditions which are achievedby means of Thyrite in inductive circuit can also be achieved by meansof a non-linear resistor in a capacitive circuit.

That is, assuming that the non-linear resistor has a magnitude ofresistance to substantially ofiset the impedance of either thecapacitive or inductive circuit to improve the power factor of thesecircuits then there will be a substantial hesitation of the current asit passes through zero.

Thus, the decrease in the rate of current increase or decrease as itpasses through zero, due to the large magnitude of resistance wheneverthe voltage is at a minimum or zero value, can be achieved with eitheran inductive. capacitive or resistive network.

In Figure 5 I have illustrated a modification of my invention whereinthe non-linear resistor 30 may be inserted between the lower stud 12 andthe front arcing horn 24. It will be noted that in the arrangement ofFigure the non-linear resistor 30 is not inserted in the circuit untilthe blow-out coil 28 is inserted in the circuit in substantially thesame manner as heretofore described in connection with Figure 1.

In the foregoing, I have described my invention in connection only withpreferred embodiments thereof. Many variations and modifications of theprinciples of my invention within the scope of the description hereinare obvious. Accordingly, I prefer to be bound not by the specificdisclosure herein, but only by the appending claim.

I claim:

An air magnetic automatic circuit interrupter being comprised of a pairof terminals, a pair of cooperating contacts and a series circuit; saidpair of cooperating contacts having an engaged and disengaged positionwith respect to each other and being electrically connected across saidterminals; said series circuit being comprised of a non-linear resistor,a blow-out coil and an arc chute; means to electrically connect saidseries circuit across said terminals when said cooperating contacts arebeing moved from said engaged to said disengaged position as a result ofthe occurrence of a fault current; said nonlinear resistance beingeffective to improve the power factor of fault current flow through saidinterrupter when said contacts are being disengaged, said non-linearresistance having the characteristics of a larger magnitude ofresistance when the voltage thereacross is at a small magnitude thanwhen the voltage is at a large magnitude to thereby be effective todecrease the rate of current increase and rate of current decrease asthe current passes through zero magnitude, to thereby aid in circuitinterruption of fault currents.

References Cited in the file of this patent UNITED STATES PATENTS1,841,091 Crago Jan. 12, 1932 2,052,318 Siegmund Aug. 25, 1936 2,292,252Thommen Aug. 4, 1942 2,295,305 Summers Sept. 8, 1942 2,546,818 CurtisMar. 27, 1951 2,586,290 Baker et al. Feb. 19, 1952 2,611,058 RawlinsSept. 16, 1952 FOREIGN PATENTS 632,718 Great Britain Dec. 5, 1949

